Professional photographers often prefer to use cameras which provide a maximum number of degrees of freedom for adjustment of the relationship between the camera lens and the film plane. Such cameras are preferred by professional photographers because they allow special effects to be achieved relating to perspective and sharpness of the photographic image by pivoting and displacing the film and lens plane relative to one another. During adjustment of the camera, the image to be photographed is viewed on an image screen in the image plane, and after lens and image screens adjustment are completed to achieve the focus and appearance desired by the photographer, the image screen is replaced by a film holder which holds the film in the image plane for exposure. Such cameras can generally be classified as of two types: studio or view cameras and field, or flat-bed cameras.
Studio cameras generally include a support bar running longitudinally from the front to the back of the camera on which slidable carriers with support standards are mounted to support an image screen and a lens holder. The distance between the image screen and lens holder of such cameras may be adjusted by moving the slidable carriers along the support bar and, additionally, each of the image screen and lens holder may be moved both translationally, in directions normal to the longitudinal support bar, and rotationally, about axes normal to the support bar.
Field cameras are most often utilized outside of the studio and the number of degrees of freedom of adjustment between the lens and image screen of these cameras may be sacrificed in the interest of providing a more rugged, compact and managable camera. Field cameras generally fold into a compact package for transport. When these cameras are unfolded, a base extends outwardly away from the image screen to provide a horizontal bed upon which a lens holder, including a lens standard, is mounted to support the lens before the image screen. Most commonly, these cameras provide at least one degree of rotational freedom for the lens about a horizontal axis parallel to the film plane by means of a hinge on the lens support assembly. Both studio and field cameras are provided with bellows extending from the image screen to the lens holder to prevent impingement of ambient light upon the image screen and film.
In addition to adjustment of perspective of the photographic image, the provision of at least one rotational degree of freedom, by pivotally connecting the image screen or lens holder to the image of an object or objects which lie in a common subject plane at varying distances from the camera. This is accomplished by application of Scheimpflug's Law, which is well known by those knowledgeable in the art, and which states that, for optimum focusing of the image in the film plane, adjustment of the camera lens and film planes should be such that the lens plane, passing through the optical center of the lens and normal to the optical axis of the lens, and a plane containing the points of the object whose images are to be focused simultaneously, should meet in a common line of intersection with the film plane.
Successfully accomplishing this arrangement of the lens, object, and image planes by trial and error adjustment can be tedious and time consuming. Particularly where the rotational axis about which the image plane or the lens may be rotated is a large distance from the optical axis of image plane or lens, rotational adjustment of the image plane or lens may be accompanied by a varied loss of focus of image points and a lateral translation of the image on the image screen. Many iterations of alternately adjusting rotation, longitudinal translation and lateral translation of the image screen and lens may be required to obtain sharp focusing together with the desired image position and perspective.
In addition to the problems of achieving focus of object points lying in a common subject plane which is not parallel to the film plane, photographers using view and field cameras are also faced with the problem of achieving an adequate zone of focus, or depth of field, about the focused plane. An increased zone of focus, or depth of field, may generally be achieved by reducing the aperture, by means of a variable opening, of the lens. For most lenses used by professional photographers, initial reduction of the aperture leads to improvement of the image quality as effects of lens aberrations are reduced. However, as reduction of the lens aperture is continued, diffraction effects degrade the image quality. Therefore, the problem facing the photographer is to determine the lens aperture which provides the necessary depths of field while also providing the best possible image quality as effected by a combination of lens aberration and aperture induced diffraction.
A number of attempts have been made in the previous art to ease the process of applying of Scheimpflug's Law in focusing field and studio cameras. These include device utilizing simple mechanical indexes applied to camera elements, such as the device disclosed in U.S. Pat. No. 3,825,938 to Koch, and devices employing a large number of sensors to record the exact locations of the camera elements in order to facilitate precise observance of the relationships mandated by Scheimpflug's Law and achieve ideal setting of the film carrier and lens carrier, such as at he device disclosed in U.S. Pat. No. 4,564,277 to Koch et al. The simpler, less expensive, mechanical index approach is not precise because of its reliance upon visual observation of mechanical analog scales and may be awkward to use because the mechanical scales are associated with different camera elements at different locations on the camera. The approach of precisely instrumenting and recording of camera adjustments is expensive and is only truly practical for use in a protected studio environment. Further, devices of the prior art incorporating each of these approaches have not been suitable for purposes of retrofitting existing studio and field cameras due to the difficulty of adapting mechanical scales or sensors to the many different parts and configurations of existing studio and field camera equipment.